The present invention relates generally to controlling a fuel cell stack, and more particularly to systems and methods for controlling cathode stack pressure during operational transients through manipulation of a backpressure valve by taking into consideration capacitance terms associated with fuel cell stack operational parameters as a way to provide a more accurate valve position instruction.
Fuel cells convert a fuel into usable electricity via chemical reaction. A significant benefit to such an energy-producing means is that it is achieved without reliance upon combustion as an intermediate step. As such, fuel cells have several environmental advantages over internal combustion engines (ICEs) and related power-generating sources. In a typical fuel cell (such as a proton exchange membrane or polymer electrolyte membrane (in either event, PEM), a pair of catalyzed electrodes are separated by an ion-transmissive medium (such as a perfluorinated sulfonic acid or an equivalent). The chemical reaction occurs when an ionized form of a gaseous reducing agent (such as hydrogen, H2) introduced through one of the electrodes (the anode) crosses the ion-transmissive medium and combines with an ionized form of a gaseous oxidizing agent (such as oxygen, O2) that has been introduced through the other electrode (the cathode). The electrons that were liberated in the ionization of the hydrogen proceed in the form of direct current (DC) to the cathode via external circuit that typically includes a load where useful work may be performed. The combination of the ions, electrons and supplied oxygen at the cathode produce water as a benign by-product. The power generation produced by the current flow can be increased by combining numerous such cells to form a fuel cell stack.
Ancillary equipment, such as compressors and associated conduit, valves, controllers or the like, are used to deliver the reactants to and from the fuel cell stack as a way to maintain the temperature, pressure, flow rate and other operational characteristics of the reactants throughout the fuel cell system. Nevertheless, it remains challenging and difficult to develop new control systems to precisely regulate the pressure of such reactants used in a fuel cell system. These challenges are particularly acute during transient operating conditions, where flow through a backpressure valve may allow larger or smaller quantities of flow than that requested by the cathode stack during such transient, resulting in inaccurate prediction of the backpressure valve position setting. Additional system complexities, such as the use of bypass valves, recirculation valves or the like, exacerbates the challenges, as do vehicular-based applications, where reliability, weight and cost are significant factors.